1. Field of the Invention
The present invention relates to a drive unit for an optical switch and particularly relates to a drive unit for an optical switch that can be applied in an optical network.
Recently, amount of data traffics transmitted on networks is sharply increasing due to rapid growth of the Internet. Therefore, a network configuration needs to be changed from a ring-type configuration to a mesh-type configuration to establish and release communication paths in a more dynamic manner. To this end, a large-scale cross-connect (XC) apparatus is required. However, currently available XC apparatuses do not have sufficient capacity (data capacity) and have limitations on electric signal processing for increased signal bit-rate. Therefore, it is difficult to build a large-scale optical switch system with currently available XC apparatuses.
MEMS (Micro-Electro Mechanical System) is one of the technologies that may be applied to such a large-scale optical switch system. FIG. 2A shows a MEMS optical switch having a two-dimensional configuration and FIGS. 1A, 1B and 2B show a MEMS optical switch of a three-dimensional configuration. In general, the MEMS optical switch of a three-dimensional configuration shown in FIG. 2B has a reduced spatial propagation distance as compared to the MEMS optical switch of a two-dimensional configuration. Accordingly, as shown in FIG. 2C, the MEMS optical switch of a three-dimensional configuration has reduced coupling loss as compared to the MEMS optical switch of the two-dimensional configuration. Therefore, the MEMS optical switch of a three-dimensional configuration is becoming of interest as a structure enabling a network of a larger scale.
FIG. 1A is a diagram showing an example of a configuration of the above-mentioned MEMS optical switch of a three-dimensional configuration. The MEMS optical switch of a three-dimensional configuration includes two optical switches 10 and 20, each including N two-axis micro-mirrors (tilt mirrors). As shown in FIG. 1B, each micro-mirror is rotatable about two axis that are mutually perpendicular. The micro-mirrors of the optical switch 10 are controlled such that light beams from optical fibers of an input optical fiber array 30 are reflected in desired directions and incident on desired micro-mirrors of the optical switch 20. The micro-mirrors of the optical switch 20 is controlled in a similar manner such that the incident light beams are reflected in desired directions and incident on desired optical fibers of the output optical fiber array 40.
Thus by controlling tilt angles of the micro-mirrors of the optical switches 10 and 20 in a three-dimensional manner, the light beams from the optical fibers of the input optical fiber array 30 are reflected on predetermined micro-mirrors of the optical switches 10 and 20 and are incident on intended optical fibers of the output optical fiber array 40. As a result, the optical fiber arrays 30 and 40 are optically connected or coupled such that optical signals can be passed from any one of the optical fiber of the input optical fiber array 30 to any optical fiber of the output optical fiber array 40.
FIG. 2A is a diagram showing an optical switch of a two-dimensional configuration. The optical switch of a two-dimensional configuration includes N2 micro-mirrors arranged in an N×N matrix. The micro-mirrors are controlled to tilt about a single axis to connect or couple optical paths between any of the N input fibers and any of the N output fibers. With such an optical switch of a two-dimensional configuration, a spatial propagation distance of a light beam taking the outermost path becomes greater than a spatial propagation distance of a light beam taking the innermost path. As can be seen in FIG. 2C, for the two-dimensional MEMS optical switch, the spatial propagation distance increases directly proportional to the number of fibers N.
FIG. 2C also shows a relationship between the spatial propagation distance and the number of fibers (N) for the optical switch of a three-dimensional configuration shown in FIG. 2B. As can be seen in FIG. 2C, the optical switch of a three-dimensional configuration of FIG. 2B is particularly advantageous when the number of fibers N exceeds fifty. It is to be noted that a signal loss is proportional to an increase of the spatial propagation distance, and therefore, an increase in the spatial propagation distance results in a reduction of transmission efficiency.
The present invention relates to a drive unit for an optical switch of a three-dimensional configuration based on a technique such as the above-mentioned MEMS technique suitable for a large-scale optical switch system.
2. Description of the Related Art
It is known to drive the MEMS optical switch of a three-dimensional configuration by means of electrostatic attractive forces produced between micro-mirrors (tilt mirrors) and predetermined electrodes. Two pairs of electrodes are provided for each micro-mirror for tilting the micro-mirror about the x-axis and y-axis. In order to control tilt angles of the micro-mirrors, voltages applied to the electrodes are varied for adjusting electrostatic forces applied to the micro-mirror. As shown in FIGS. 1A and 1B, tilt angles of micro-mirrors of an input-side optical switch and micro-mirrors of an output-side optical switch are controlled to redirect light beams from any one of the input ports towards any one of the output ports.
The optical switch of such a configuration is known from reports made by χ ros (now a part of Nortel) or Lucent Technologies Inc. at various conferences and in press-releases. However, no suggestions have been made about a configuration of a drive circuit part for applying voltages to electrodes. It can be simply assumed that a single drive circuit should be provided for each of the electrodes. Therefore, such a configuration of a driving circuit part is to be understood as a related art.
FIG. 3 is a schematic diagram showing an example of a drive unit of an optical switch of the related art. In this example, a control circuit 100 selects a mirror MM to be controlled. Then the control circuit 100 looks up a memory table to read out digital signals (voltage information for achieving a desired angle) that are associated with tilt angles of the mirror MM in a one-to-one relationship. Then, the control circuit 100 outputs the obtained digital signals. The digital signals are converted into analog signals in D/A converters 121, 122, 123 and 124. Drive circuits (DRV) 131, 132, 133 and 134 amplify the analog signals and supply corresponding voltages to each electrode (XR#1, XL#1, YU#1, YD#1). The tilt angles of the micro-mirror MM are adjusted in accordance with the supplied voltages. Accordingly, optical paths of the light beams can be redirected.
FIG. 4 is a diagram showing an example of a drive unit of an optical switch of the related art for an optical switch of an N-channel configuration. The optical switch has N micro-mirrors and thus N sets of D/A converters and drive circuits DRV are required. In the figure, the configuration of an input side system 10 is shown, but it is to be understood that the configuration of an output side system 20 is similar to the input side system 10.
In general, the MEMS optical switch of the above-described type using electrostatic attractive forces requires a voltage in a range of several tens to several hundreds of volts to achieve a maximum tilt angle. A supply voltage of the drive circuit should be of the same range. Moreover, with the drive unit of the related art shown in FIG. 4, 4×N drive circuits are required for each of the N mirrors. Therefore, an overall size and consumption power of the entire optical switch including the drive circuit becomes unacceptably large.